1. Field of the Invention
The present invention generally relates to a method for forming a multilayer electronic device. More particularly, the present invention relates to a method for forming a multilayer electronic device wherein a thin molecular layer is deposited on a substrate. Still more particularly, the invention relates to a method for forming a multilayer electronic device wherein a metal atoms or ions are deposited on the thin molecular layer to form a metallic layer thereon.
2. Description of the Prior Art
There is increasing commercial interest in electronic devices fabricated using molecular monolayers or a small number of molecular layers of materials. Examples of materials useful in thin molecular layers are alkanethiols, such as mercaptohexadecanoic acid and nitrobenzenethiol. Such thin molecular layers can be applied to or deposited upon substrates using techniques such as thiol or isonitrile attachment to metals or silane coupling to oxides, or by alternate techniques such as Langmuir-Blodgett deposition.
In electronic devices, it is frequently necessary to make electrical contact with thin molecular layers. In particular, it is also important to provide electrical contact top both sides of a thin molecular layer between opposing metal surfaces or substrates. Such devices are typically formed by applying a thin molecular layer to a metal substrate or other conducting substrate followed by application of a metallic layer to the exposed surface of the thin molecular layer. The first step seldom presents manufacturing problems since there are a number of approaches, including liquid or vapor phase self-assembly chemistry, such as using thiol, isonitriles, or Langmuir-Blodgett deposition, vapor deposition or solvent casting whereby the thin molecular layers attach securely to the metal substrate. However, the second step, application of the metallic layer to the exposed surface of the thin molecular layer, is problematic because the metal atoms applied to the surface can infiltrate it and cause the formation of electrical short circuits in the thin molecular layer. In conventional deposition processes, the incoming metal atoms or ions can have sufficient energy and mobility to pass through the molecular layer to wet the underlying metal. Infiltration is a particular problem when surface energy differences between the molecular layer and underlying metal promote migration or deposition of adatoms to the underlying conducting substrate.
One means of addressing the problem of infiltration or penetration of metal atoms or ions into the thin molecular layer has been to employ reactant groups at the surface of the layer capable of reacting with or binding to the metal atoms or ions being deposited there. Another means of addressing the problem has been to reduce the temperature of the substrate and the thin molecular layer to reduce the mobility of incoming metal atoms or clusters at the surface of the layer.
It would be highly desirable to have a method for depositing metal atoms or ions on a thin molecular layer on a substrate to form a multilayer electronic device. It would further be desirable to have a method for depositing metal atoms or ions on a substrate having a thin molecular layer wherein defects are substantially not present and/or infiltration of metal adatoms into the thin molecular layer is substantially prevented. It would still be further desirable to have a method for depositing a metallic layer on a substrate having a layer of an electroconductive electroactive, or electrooptic organic material.
According to the present invention, there is a method for forming a multilayer electronic device. The method has the following steps: a) depositing a thin molecular layer on an electrically conductive substrate and b) depositing metal atoms or ions on the thin molecular layer at an angle of about 60 degrees or less with respect to the plane of the surface of the thin molecular layer.